API Plans

Plan 21

Description: Plan 21 is recirculation from pump discharge

through an 1/8” minimum flow control orifice (when

necessary), and seal flush cooler, then into the seal chamber.

Objective: Cool the process in the seal chamber, improving

lubricity and increasing the vapor margin. Reduce coking.

Advantages: Provides cooling through a seal flush cooler.

When used with a close‐clearance throat bushing, it can raise

the pressure in the seal


Recommended over

Plan 23 when used in

viscous applications that

may clog seal flush


Note: Plan 23 is the preferred plan due to

high heat loads put on the seal flush

cooler when using Plan 21.